Fungus Gnat - Management

Management

Fungus gnats are typically harmless to healthy plants - and humans - but can inflict extensive damage to seedlings; their presence can be indicative of more serious problems. In houseplants, the presence of fungus gnats may indicate overwatering; they may be feeding on roots that have sat in drain water too long and are thus rotting, or the gnats may be attracted to fungus growing in saturated topsoil. Consequently, allowing the soil to dry may reduce their numbers.

Other methods of management may include the following:

• Placing about half an inch of sterile sand on top of the soil around plants; the fungus gnats can't get back to the soil and the larvae can't escape. Indoor mulch may also be effective.

• Introducing Hypoaspis miles mites or applying the biological larvicide Bacillus thuringiensis (subspecies israelensis) to kill the gnats in their larval stage; the larvacide must be applied weekly as a soil drench for 4–5 weeks.

• Annually drenching the soil in an insecticidal soap; neem oil may be used as a repellent when diluted 1 teaspoon per litre of water and applied 300 ml per square meter of soil (4 teaspoons per US-gallon of water, applied 3 avoirdupois ounces per international square foot). Detergents and the nicotine from tobacco brewed into a toxic tea are used by some people to control fungus gnats.
• Also to manage these insects, leave a small cup of vinegar out. The gnats will fly into it and drown.